Surge suppressors

Jim Lux James.P.Lux at jpl.nasa.gov
Fri Nov 1 18:06:15 EST 2002


At 04:52 PM 11/1/2002 -0500, Robert G. Brown wrote:
>On Fri, 1 Nov 2002, Jim Lux wrote:
>
> >
> > Circuit Rating/Receptacle rating
> > 15/not over 15
> > 20/15 or 20
> > 30/30
> > 40/40 or 50
> > 50/50
>
>I'm trying to understand that.  Are they saying you can't use a
>20A-rated receptacle on a 15A, 14Ga wire circuit?  I'd have thought it
>was the exact opposite, that it has to be at LEAST 15 (just like the 40
>A circuit needs a receptacle that is at LEAST 40).

Yep, confusing... Here's my guess.. it's a historical holdover from when 
all branch circuits were 15A.  Note that the 40 A circuit can have a 40 or 
50 amp receptacle.  There's also some special rules for branch circuits 
that have cord connected appliances that aren't likely to be moved (i.e. 
refrigerators), and so forth...

By definition, a device that has a 15A plug on it can't consume more than 
12A, by design and code(the rating is for normal use, not the fault 
situation, where the current is hundreds or thousands of amps).  The rule 
for 15A outlets is on 20A branch circuits with more than one receptacle, so 
clearly, the idea is that you're going to connect more than one load on 
that branch circuit.


> > (B)(2) Total Cord-and-Plug-Connected Load
> > Where connected to a branch circuit supplying two or more receptacles or
> > outlets, a receptacle shall not supply a total cord-and-plug-connected 
> load
> > in excess of the maximum specified in table ...
> >
> > circuit rating/recep rating/max load
> > 15 or 20/15/12
> > 20/20/16
> > 30/30/24
>
>This makes sense, although the code should provide protection against
>any load that doesn't blow the breaker, anywhere or way it is plugged in
>(because such a load, sustained, can always occur by accident), max
>sustained INTENTIONAL load should be lower by design to allow for things
>like poor power factors and different things being plugged into the
>different receptacles.
>
>This is why I still just don't understand permitting a 15 A receptacle
>on a 20 A branch, where an 19 A sustained accidental overload (caused by
>e.g. a partial short circuit) could burn the receptacle without blowing
>the breaker.

I think the "credible fault" is a massive overload.. a "listed" device 
shouldn't be able to develop a partial short of 19A...


>Sigh.  Now I'm puzzled.  Any insight?
>
>BTW, did you find the code online (I'd love the URL) or do you have a
>paper copy.  IS the code online?

Interesting story there.. it's not online... The "code" is copyrighted by 
the NFPA.  Someone in Texas posted the code online, and was sued by NFPA. 
His defense was that since the NEC was defined as the local municipal 
electrical code (by reference), and that, at the time, the law in Texas 
said that laws,ordinances,etc. cannot be copyrighted, or must be freely 
reproducible (since we're all subject to them, it isn't "fair" to require 
someone to pay to see the rules they're subject to.. a valid point in my 
opinion.) I don't recall how it came out in the end.

In the back of the written copy I have, there's a bunch of stuff about how 
a municipality that might adopt the NEC (by transcription, as opposed to 
reference) can make copies of the code for public use and display but not 
distribution during the law or rulemaking process(i.e. you could make a 
copy to have available for public reference at city hall or a library), but 
that they can't publish it online, etc. nor, and this is interesting, can 
they reproduce the index.  Furthermore, they have to pay a royalty for the 
copies they do reproduce.

There was a relatively famous case by West Publishing (who make a business 
of publishing laws, annotated codes, court decisions, and the like) and the 
State of California, when the State wanted to put the law on line.  Turns 
out that while the law itself isn't copyrighted, West had the copyright on 
the particular publication format, and, more important in a practical 
sense, the citation format.  If you needed to go look something up, odds 
are that the citation reference you were looking at was in West's peculiar 
format, and it made it quite difficult to go find the relevant data, since 
the state had never compiled an index of things in their "real name" (case 
numbers and captions, for instance), just in the West citation form 
referring to the published book and page numbers(things like Cal2ndRpt 
pp405-...)

For what it's worth, the California laws and most regulations (except some 
that are copyrighted, like the Title 24 energy stuff) are all on line now 
(http://www.leginfo.ca.gov/)

By the way, the Uniform Building Code is handled the same general way as 
the NEC, as are most, if not all, ANSI and IEEE standards, but, in general, 
they don't affect quite as many people. The standards organizations (one of 
which I am a member) do point out that if one protects copyright one can 
have a "controlling authority" for the "one true version", since one 
couldn't publish a modified version and call it the standard.

Personally, I think that any rule that the "public" is subject to should be 
freely available and reproducible, but, a requirement that one agree to 
certain formatting and presentation requirements is probably reasonable 
(i.e. you can't change the intent or meaning by "editing" or "revision" or 
"excerpting").






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